The present invention relates to antenna elements used in active array antenna systems.
For many active array applications the radiating element needs to have low RF losses, operate across a wide frequency band, and be inexpensive to fabricate.
A conventional flared notch radiator has only a single port for both transmit and receive. In an active array antenna each radiator is connected to a transmit/receive (T/R) module with separate transmit and receive controls. The T/R module typically contains its own duplexing network to route the transmit and receive signals. This duplexing network generally includes a 3-port circulator which adds to the cost and physical size.
In a typical active array antenna, the circulator and T/R module are packaged together in a metal housing. To reduce the cost of the metal packaging for the array, four pairs of single channel modules and circulators are assembled into the housing. This limits the shape and size of the antenna aperture that can be designed per given area because the aperture can by populated only with elements in groups of four (four elements for each four channel housing). Integrating the circulator into the radiator would eliminate this additional housing and allow more cost effective and flexible implementation of single channel modules.
Another disadvantage with the conventional approach occurs when this larger four channel assembly is attached to the cold plate. A larger cold plate is needed to mechanically support these long assemblies even though only the few active components in the modules require cooling in order to perform reliably and optimally. Integrating the circulator into the radiator would result in a shorter cold plate and module which in turn results in a shorter and lighter antenna.
The radar cross section (RCS) performance of the antenna is related to the active impedance of each individual radiating element. Placing a coaxial adapter between the radiator and the module as in the conventional active array contributes an additional mismatch and thus degrades the performance. Moving the adapter behind the circulator and then using a four port circulator would isolate the adapter and modules mismatches away from the aperture.
It is therefore an object of the present invention to provide a radiator element which integrates a signal duplexing arrangement, thereby permitting a reduction in the size and cost of the corresponding T/R module, while improving the active impedance match of the radiating element.